as for flushing, ive seen a vid of a cat doing it online, but i imagine that would be rather hard to teach. remember, theyre cats. if you suceed with this, be glad you got them using a toilet.

Step 1: Set the Mood...

cats are creatures of habit, and generally react badly to majior changes of any kind. to start with, move kittys litterbox to the bathroom if its not already there. leave next to the toilet for at least two weeks, if the litterbox was in a completely different area of the house, expect an accident or two if your cat is older. say no firmly, and place them gently in the litter box. some cats are particularly stubborn, and might need to be shut in the bathroom with food and water for a night.

Step 2: Take It Up a Notch...

now we need to get kitty used to the idea of peeing in something thats not on the ground. search around for a crate / box / step stool / etc. that will raise the littlerbox up to the height of the toilet rim. dont forget to add something for kitty to use as a step. if this fails at first, do this in two steps, raising the litter box 6 inches at a time. again, wait two weeks for your poor confused puss to get used to the idea.

Step 3: Almost There...

now move the litterbox onto the toilet seat. if you only have one bathroom, make sure you replace the litterbox back on the toilet seat when youre done. consistency is key. once again, leave for two weeks.

Step 4: Now for the Tricky Part...

for this youll need an in - toilet litter container. you have a few options here.

option 1: make one. you could use all sorts of things, but ive found that the cheap foil baking pans work best, as you can bend them to fit inside the rim. if you plan to use this option, i would suggest switching their regular litter pan to one of the large roast sizes in the beginning. (step 1)

option 2: find a childrens potty training toilet that has a removable bowl you put on the big toilet.

option 3: buy a litter pan specially made for use in a toilet. these can be found relatively cheaply online.

whatever you use, DONT FORGET to tape it down with some good tape. (duct tape?) you dont wanna know how pissed you puss would be if he fell in.

The last step is too rushed!Once the litter inside the toilet has been there for two weeks, you should cut a small hole in the middle, wait until the cat has adapt.Then cut a larger hole, and wait.Then an even larger hole.All the while reducing the amount of litter. This is how the cat will get accustom to the toilet.

Great Instructable.
I would advise against doing this with smaller kittens, since they could accidentally be flushed into the sewers where they would ultimately come in contact with some toxic waste, grow to an enormous size and terrorize a large metropolitan Japanese city.

this is a very cool ible; and it is cool that you can train a cat to use a toilet... that said I'm not too sure I'd wanna' share my toilet with my cat, not the least of which would be coming home from work to find cat logs in the toilet. ;-)

Hmmm - I tried this with my tom cat. He REFUSED to stand on the edge of the toilet for step 4 and, instead, stood in the little tray inside so that he nearly fell in several times. This, however, did not stop him from peeing up there. Once I took the tray out of the toilet, though, he stopped using the toilet and did all his business in the tub.
Back to the box.
I like the idea of a kiddy potty chair - that might help - the toilet training kits for cats have a sort of flat bottom in the pan you put on the toilet. With the kiddy seat he might not be able to get good footing!
What a blessing a toilet-trained cat would be!

maybe if you thought to get your cat spayed she would stop wanting to out and get laid and meow all the time it's not rocket science dude- there are lots of low cost spay neuter clinics if you knew anything about cats you would have figured this out.